Featured Image: A salmon in a stream on the Oregon coast. Photo credit: Conrad Gowell
Authors: S. Wistbacka, A. Heinonen, and G. Bylund
Flintstones vitamins are generally marketed for children, but should fish be taking them too? Thiamine (vitamin B1) deficiency in fish, especially species of salmon, is a widespread issue with serious implications, as this vitamin is an integral compound required by virtually all living organisms. Vitamin B1 deficiency can lead to an array of negative health outcomes for salmon, which collectively manifest as the condition known as thiamine deficiency complex. This condition inhibits many salmon and other anadromous fish (those that migrate from the oceans to rivers to spawn) from spawning, posing a major problem for their long-term survival.
Yolk-sac fry mortality is a major symptom of thiamine deficiency complex for both wild and farmed salmon, which has drawn researchers to discover the causes of this affliction. Expansive efforts from groups found across the globe are currently underway with this very goal in mind. However, a pivotal finding by Wistbacka and coworkers in 2002 helped lay the foundation for research into potential causes of thiamine deficiency complex. This group of scientists discovered a link between the occurrence of vitamin B1 deficiency and the presence of an enzyme that degrades thiamine, called thiaminase, in the fish preyed on by Baltic salmon.
Wistbacka & co examined the guts of vitamin B1-deficient Baltic salmon and herring for thiaminase activity by measuring both the amount of the thiaminase present and the rate at which thiamine was destroyed by the enzyme. Their goal was to find a link between the existence and activity of the enzyme and the prevalence of thiamine deficiency complex. The rationale for this research approach stemmed from previous findings, based on animals other than fish, that the consumption of prey high in thiaminase by predators caused thiamine deficiency. Baltic salmon also proved to be an ideal fish to study because nearly their entire diet was made up of Baltic herring, which makes it unlikely that thiaminase in the salmon would arise from any other prey species.
Intriguingly, the researchers found that the average thiaminase activity levels of Baltic herring were the same as those in the stomach contents of salmon that suffered from thiamine deficiency complex. As mentioned earlier, because herring encompassed nearly the entirety of the diet of Baltic salmon, this was strong evidence that high thiaminase activity levels in salmon GI tracts were driven by herring consumption. Overall, this finding demonstrated a correlation between salmon thiaminase levels and thiamine deficiency complex.
This study, and others like it, have become the impetus for much of the current scientific research on vitamin B1 deficiency in salmon found in different environments. Many present studies have focused on whether other salmon prey species are similarly high in thiaminase and if the thiaminase in them is the sole cause of thiamine deficiency complex, or if other details are involved. Although Wistbacka & co demonstrated a correlation between herring thiaminase levels and thiamine deficiency complex in salmon, causation between these factors was not proven. Contemporary studies on thiaminase activities in salmon prey species therefore aim to prove definitively that this enzyme causes vitamin B1 deficiency.
As our planet is relentlessly struck by the impacts of climate change, salmon and other spawning fish are increasingly stressed by extreme heat and drought, which lower river water tables and push these animals to their limits of survival. The difficulties faced by vitamin B1-deficient salmon are magnified by these ecological pressures and multitudes of others, such as infections by microbial pathogens and high river water temperatures. The authors of this study are to be commended for helping lay the groundwork for a main area in the realm of thiamine deficiency researcher; however, many questions remain, such as which salmon prey species contribute the most to salmon thiaminase levels and what environments will be impacted the most severely by thiamine deficiency complex. Therefore, the importance of continuing research into the causes and consequences of thiamine deficiency complex, and potential solutions to this problem, cannot be understated.
A Historical Link Between Thiamine Deficiency in Salmon and the Presence of Thiaminase in their Prey by Kelly Shannon is licensed under a Creative Commons Attribution 4.0 International License.